Last month, this column addressed estrus detection. Now, let’s look at the ins and outs of semen inseminations and timing. How many inseminations and when to give them are highly related to farrowing success and producing large litters.
So let’s start with artificial insemination timing. The biggest limit to fertility during AI is the eight-hour period from ovulation to fertilization. Introducing sperm to aged eggs after this time results in fewer fertilized eggs, normal embryos, fetuses and pregnancies. The objective of insemination is to establish a functional sperm reservoir with sperm waiting for the egg to arrive. While some sperm arrive within minutes of insemination, most reach the reservoir within hours.
The slower arriving sperm become capacitated and are better able to fertilize an egg and survive in the female tract. It takes about four hours for sperm to establish themselves. To get the uterus to move semen and to effectively establish the reservoir requires more than 5 cc and proper sperm numbers. Excessive leakage reduces volume, sperm numbers and fertility. Studies show that single inseminations occurring within 24 hours before ovulation result in the highest pregnancy rates and largest litters. European data shows that the insemination window starts about 24 hours before ovulation (a process that takes about three hours) and extends for eight hours past ovulation. This can change when using low-fertility semen. With frozen semen, the window is only four hours around ovulation. Research suggests that even with high-fertility semen, the insemination must hit a precise window for maximum fertilization and fertility.
As for double inseminations, much of the data shows that gilts and sows receiving double inseminations have greater fertility than females inseminated only once. However, more is not always better, as triple inseminations do not statistically improve fertility. In some cases it can actually reduce fertility if the last insemination occurs too late after ovulation or after fertilization has already occurred.
New technologies, such as intrauterine insemination, that were designed to improve fertility and reduce the required sperm cells produce maximum fertility only with double inseminations. This is clearly a way to compensate for variation in ovulation times.
So, it seems that under any situation, identifying the 24- or 12-hour time periods prior to ovulation can pay off in terms of reproductive performance. Researchers have identified ovulation time using ultrasound scans of the ovaries, while others can predict ovulation with blood hormone levels. Some have removed variation by attempting to synchronize estrus and ovulation, as well as using fixed-time AI.
Yet the only reliable and practical marker remains estrus, and that alone is probably not good enough. Estrus is highly variable in both the onset and duration. It can last anywhere from one to three days. In weaned sows, the time from weaning to estrus is related to estrus duration and the time from estrus onset to ovulation. It can vary as much as 24 hours. In young gilts, estrus is typically shorter than in more mature females.
Characterizing estrus duration patterns in weaned sows, cyclic and young gilts is possible and can be a powerful tool to perform precision AI. For example, if selected females are used to capture representative measures for estrus onset and duration, those animals can serve as models for precision AI. Since ovulation is known to occur 60 percent to 70 percent into the estrus period, it’s possible to use models to optimize AI timing. This exercise can help evaluate whether protocols such as delayed or skipped breedings are good practices for your herd. Regardless, assessing the fertility data for gilts and sows based on their estrus duration or wean-to-estrus interval can help you fine-tune your breeding protocols.